Paleontology

Classic descriptions and a previous reconstruction of the Middle Triassic ray-finned fish Birgeria stensioei ALDINGER, 1931 from the Besano Formation (= Grenzbitumenzone) of Monte San Giorgio (Canton Ticino, Switzerland) and Besano (Lombardy, Italy) relied either on poor material or on a single specimen only. This study of B. stensioei is based on 67 specimens from that region in the Southern Alps including the lectotype of B. stensioei. The reappraisal of B. stensioei indicates that this species differs from the other known species of the genus Birgeria in several respects, most notably in the arrangement of the pterygiophores of the dorsal fin. B. stensioei is also distinct to certain other species of Birgeria in having a largely unossified brain case. Furthermore, the palatoquadrate of B. stensioei is ossified as the autopalatine, the metapterygoid and the quadrate, which are always found separate. An ossified autopalatine and metapterygoid was not described in Birgeria so far. A dermohyal is developed in B. stensioei and this bone is probably also present in the other species of the genus Birgeria.

For the first time, the otic capsule (proötic and opisthotic) of a Triassic ichthyosaur is described, based on a specimen of Mixosaurus cf. cornalianus from the Grenzbitumenzone of Monte San Giorgio, Switzerland. The otic capsule of Mixosaurus differs from that of more highly derived ichthyosaurs by several features, which are mainly related to the much higher degree of ossification found in Mixosaurus. The proötic is extensively ossified and shows an anteroventral facet for contact with the basisphenoid, a crista prootica lateralis, a foramen completely enclosed by bone for the exit of the nervus facialis, and a posterior sutural contact with the opisthotic, thus closing off the lateral wall of the internal ear capsule. The proötic also forms the anterior margin of a well ossified fenestra vestibuli and has a posterodorsal articulation facet for the supraoccipital. The opisthotic has an elongate, anteroposteriorly compressed, plate-like processus paroccipitalis and shows a well ossified crista interfenestralis, forming the posterior margin of the fenestra vestibuli and the anterior margin of the foramen metoticum. The anterodorsal contact with the supraoccipital is well defined. For all these features, Mixosaurus is much closer to basal amniotes and basal diapsids, such as Captorhinus, Procolophon or Youngina than to more highly derived ichthyosaurs. The new data on the otic capsule of Mixosaurus are corroborated by the braincase of another Middle Triassic ichthyosaur, Phantomosaurus. It can be assumed that the reported features of the Mixosaurus braincase, which are unusual compared with other known ichthyosaurs, could be plesiomorphies retained from an unknown ichthyosaur ancestor, that is representative of the grundplan of ichthyosaurs. However, in the absence of further material the possibility that some features of the mixosaurid otic capsule are autapomorphic within ichthyosaurs can not be excluded. Anhand eines Exemplares von Mixosaurus cf. cornalianus (BASSANI, 1886) aus der Grenzbitumenzone des Monte San Giorgio (Schweiz) wird erstmals die Ohrkapsel (Prooticum und Opisthoticum) eines triassischen Ichthyosauriers beschrieben. Die Ohrkapsel von Mixosaurus unterscheidet sich von den Ohrkapseln höher abgeleiteter Ichthyosaurier in vielen Merkmalen, die im Wesentlichen auf den deutlich stärkeren Verknöcherungsgrad zurückzuführen sind. Das Prooticum ist umfangreich verknöchert und besitzt eine anteroventrale Facette für das Basisphenoid, eine Crista prootica lateralis, ein vollständig ossifiziertes Foramen zum Austritt des Nervus facialis und eine posteriore Sutur mit dem Opisthoticum, wodurch die Ohrkapsel lateral knöchern geschlossen wird. Das Prooticum bildet den anterioren Rand einer wohlverknöcherten Fenestra vestibuli und zeigt eine posterodorsale Facette für das Supraoccipitale. Das Opisthoticum hat einen langen, anteroposterior abgeflachten Processus paroccipitalis und eine gut ossifizierte Crista interfenestralis, die den posterioren Rand der Fenestra vestibuli und die anteriore Umgrenzung des Foramen metoticum bildet. Der anterodorsale Kontakt zum Supraoccipitale ist klar definiert. In all diesen Merkmalen ähnelt Mixosaurus viel mehr basalen Diapsiden und basalen Amnioten wie Captorhinus, Procolophon und Youngina als abgeleiteten Ichthyosauriern. Die neuen Daten über die Gehörkapsel von Mixosaurus finden Bestätigung durch Beobachtungen am Hirnschädel von Phantomosaurus, einem weiteren mitteltriassischen Ichthyosaurier. Es kann angenommen werden, dass die meisten ungewöhnlichen Charakteristika der Mixosaurus- Gehörkapsel von unbekannten Vorfahren ererbte Plesiomorphien sind und den Grundplan der Ichthyosaurier widerspiegeln. Ohne weiteres Vergleichmaterial kann die Möglichkeit, dass einige Gehörkapsel-Merkmale von Mixosaurus innerhalb der Ichthyosauria autapomorph sind, jedoch noch nicht ausgeschlossen werden.

Most reports of Paleozoic and Mesozoic vertebrates from Venezuela are anecdotical, with few detailed descriptions of mostly ‘fish’ groups. Synapsids (e.g., mammals) are totally unknown, and dinosaurs are only reported from the La Quinta Formation. At least 14 formally recognized geological formations contain fossil vertebrates, most from the Central and Western parts of the country. In the Devonian there is a significant contrast between the vertebrates of Venezuela and Colombia and those of more southern parts of South America. Marine reptiles are present in a few localities in western Venezuela, and are very fragmentary, with one exception. A mosasaur from the Cretaceous La Luna Formation, reported here for the first time, is the most complete vertebrate (tetrapod) from the Cretaceous of Venezuela, and includes a partial skull and a few postcranial remains. Berichte über paläozoische und mesozoische Wirbeltiere von Venezuela sind weitgehend anekdotisch, mit der Ausnahme von wenigen ausführlichen Beschreibungen, die meistens ‘Fischgruppen’ betreffen. Synapsiden (z.B. Mammalier) sind völlig unbekannt und Dinosaurier sind nur aus der La Quinta Formation nachgewiesen. Mindestens 14 formell anerkannte geologische Formationen haben fossile Wirbeltiere geliefert, meistens aus den zentralen und westlichen Landesteilen. Im Devonium fällt zwischen den Wirbeltieren aus Venezuela und Kolumbien sowie jenen aus südlicheren Regionen Südamerikas ein wesentlicher Gegensatz auf. Marine Reptilien sind aus wenigen Lokalitäten von Westvenezuela nachgewiesen. Diese Funde sind mit einer Ausnahme sehr fragmentarisch. Über einen Mosasaurier aus der kretazischen La Luna Formation wird hier erstmals berichtet. Dabei handelt es sich um das vollständigste Wirbeltier (Tetrapode) aus der Kreide von Venezuela. Das Material umfasst einen unvollständigen Schädel und wenige postcraniale Reste.

The Paleocene–Eocene Taleh Zang Formation of the Zagros Basin is a sequence of shallow-water carbonates. We have studied carbonate platform, sedimentary environments and its changes based on the facies analysis with particular emphasis on the biogenic assemblages of the Late Paleocene Sarkan and Early Eocene Maleh kuh sections. In the Late Paleocene, nine microfacies types were distinguished, dominated by algal taxa and corals at the lower part and larger foraminifera at the upper part. The Lower Eocene section is characterised by 10 microfacies types, which are dominated by diverse larger foraminifera such as alveolinids, orbitolitids and nummulitids. The Taleh Zang Formation at the Sarkan and Maleh kuh sections represents sedimentation on a carbonate ramp.

The deepening trends show a gradual increase in perforate foraminifera, the deepest environment is marked by the maximum occurrence of perforate foraminifers (Nummulites), while the shallowing trends are composed mainly of imperforate foraminifera and also characterised by lack of fossils in tidal flat facies.

Based on the facies changes and platform evolution, three stages are assumed in platform development: I; algal and coralgal colonies (coralgal platform), II; coralgal reefs giving way to larger foraminifera, III; dominance of diverse and newly developing larger foraminifera lineages in oligotrophic conditions.

In order to examine the evolution of the phalangeal formula in a diverse clade of turtles, including hyperphalangy as a rare condition in this group, we studied 210 specimens representing all extant genera of Trionychidae and their sister taxon, Carettochelyidae. Both groups consist of highly aquatic species with elongated autopods that are either paddle-like (Trionychidae) or transformed to flippers (Carettochelyidae).

A major gap in our knowledge of the evolution of marsupial mammals concerns the Paleogene of the northern continents, a critical time and place to link the early history of metatherians in Asia and North America with the more recent diversification in South America and Australia. We studied new exceptionally well-preserved partial skeletons of the Early Oligocene fossil Herpetotherium from the White River Formation in Wyoming, which allowed us to test the relationships of this taxon and examine its adaptations. ...

Dinosaur remains are exceptionally scarce in northern South America and Jurassic faunas from this area are particularly poorly known. We provide descriptions of new dinosaur specimens from a bonebed in the La Quinta Formation (Early or Middle Jurassic) of western Venezuela. The specimens are disarticulated and associations of elements are rare, but at least two distinct taxa appear to be present. Ornithischian dinosaurs are identified on the basis of isolated teeth and a distal tibia. The teeth represent a non- ...

Sutures, joints that allow one bone to articulate with another through intervening fibrous connective tissue, serve as major sites of bone expansion during postnatal craniofacial growth in the vertebrate skull and represent an aspect of cranial ontogeny which may exhibit functional and phylogenetic correlates. Suture evolution among hystricognath rodents, an ecologically diverse group represented here by 26 species, is examined using sequence heterochrony methods, i.e. event pairing and PARSIMOV . Although minor nuances in suture closure sequence exist between species, the overall sequence was found to be conserved both across the hystricognath group and, to an increasing degree, within selected clades. At species level, suture closure pattern exhibited a significant positive correlation with patterns previously reported for hominoids. Patterns for most clades revealed the first sutures to close are those contacting the exoccipital, interparietal, and palatine bones. Heterochronic shifts were found along 19 of 35 branches within the hystricognath phylogeny. The number of shifts per node ranged from one to seven events and, overall, involved 21 of 34 suture sites. The topology generated by parsimony analyses of the event pair matrix yielded only one grouping that was congruent with the evolutionary relationships, compiled from morphological and molecular studies, taken as framework. Sutures contacting the exoccipital displayed the highest levels of most complete closure across all species. Level of suture closure is negatively correlated with cranial length ( P < 0.05). Differing life history and locomotory strategies are coupled in part with differing suture closure patterns among several species. Fig. 1 Compound phylogeny featuring species investigated: 26 Hystricognath taxa and five outgroup species selected from Myodonta, Sciurida and Castorimorpha. Number of recorded heterochronic shifts, or changes in timing of suture closure events following the consensus approach of PARSIMOV, denoted under each branch. Suture heterochrony in rodents, L. A. B. Wilson and M. R. Sánchez-Villagra

The tetrapod limb provides several examples of heterochrony-changes in the timing of developmental events. These include species differences in the sequence of skeletal chondrogenesis, in gene transcription in the developing limbs, and in the relative time at which forelimb and hind limb buds develop. Here, we examine (i) phylogenetic trends in limb heterochrony; (ii) changes in developmental mechanisms that may lead to heterochrony; and (iii) the possible role that heterochrony plays in generating adaptive traits. We analyze the published literature and present preliminary data on turtle (Emys orbicularis) and bat (Rousettus amplexicaudatus) limb development. Teleosts, marsupials, and some urodeles show extreme timing differences between forelimb (or pectoral fin) and hind limb (or pelvic fin) development; this heterochrony may, in some cases, be adaptive. Published data on limb chondrogenesis reveal sequence elements that are strongly conserved (possibly owing to constraints); and others that vary between higher taxa (for unknown reasons). We find little evidence that chondrogenic sequences are modified by selection for limb functional traits. There are a few examples of developmental mechanisms that may be modified under heterochrony to produce adaptive changes in the limb (e.g. some cases of hyperphalangy or limb reduction). In conclusion, numerous examples of limb heterochrony have been recorded. However, few cases are obviously adaptive. Indeed, current data and methodologies make it difficult to identify the developmental changes, or selective pressures, that may underlie limb heterochrony. More integrative studies, including studies of heterochrony within populations, are needed to assess the role of timing shifts in limb evolution.

Background Here we provide the most comprehensive study to date on the cranial ossification sequence in Lipotyphla, the group which includes shrews, moles and hedgehogs. This unique group, which encapsulates diverse ecological modes, such as terrestrial, subterranean, and aquatic lifestyles, is used to examine the evolutionary lability of cranial osteogenesis and to investigate the modularity of development. Results An acceleration of developmental timing of the vomeronasal complex has occurred in the ...

The vast mammal diversity of the Neotropics is the result of a long evolutionary history. During most of the Cenozoic, South America was an island continent with an endemic mammalian fauna. This isolation ceased during the late Neogene after the formation of the Isthmus of Panama, resulting in an event known as the Great American Biotic Interchange (GABI). In this study, we investigate biogeographic patterns in South America, just before or when the first immigrants are recorded and we review the temporal and geographical distribution of fossil mammals during the GABI. We performed a dissimilarity analysis which grouped the faunal assemblages according to their age and their geographic distribution. Our data support the differentiation between tropical and temperate assemblages in South America during the middle and late Miocene. The GABI begins during the late Miocene (~10-7 Ma) and the putative oldest migrations are recorded in the temperate region, where the number of GABI partic...